1. Field of the Invention
The present invention pertains generally to steam desuperheaters and, more particularly, to a uniquely configured valve element for use in a spray nozzle assembly for a steam desuperheating device. The nozzle assembly is specifically adapted for creating a substantially uniformly distributed spray of cooling water for spraying into a flow of superheated steam in order to reduce the temperature thereof.
2. Description of the Related Art
Many industrial facilities operate with superheated steam that has a higher temperature than its saturation temperature at a given pressure. Because superheated steam can damage turbines or other downstream components, it is necessary to control the temperature of the steam. Desuperheating refers to the process of reducing the temperature of the superheated steam to a lower temperature, permitting operation of the system as intended, ensuring system protection, and correcting for unintentional deviations from a prescribed operating temperature set point.
A steam desuperheater can lower the temperature of superheated steam by spraying cooling water into a flow of superheated steam that is passing through a steam pipe. Once the cooling water is sprayed into the flow of superheated steam, the cooling water mixes with the superheated steam and evaporates, drawing thermal energy from the steam and lowering its temperature. If the cooling water is sprayed into the superheated steam pipe as very fine water droplets or mist, then the mixing of the cooling water with the superheated steam is more uniform through the steam flow.
On the other hand, if the cooling water is sprayed into the superheated steam pipe in a streaming pattern, then the evaporation of the cooling water is greatly diminished. In addition, a streaming spray of cooling water will pass through the superheated steam flow and impact the opposite side of the steam pipe, resulting in water buildup. This water buildup can cause erosion and thermal stresses in the steam pipe that may lead to structural failure. However, if the surface area of the cooling water spray that is exposed to the superheated steam is large, which is an intended consequence of very fine droplet size, the effectiveness of the evaporation is greatly increased.
In addition, the mixing of the cooling water with the superheated steam can be enhanced by spraying the cooling water into the steam pipe in a uniform geometrical flow pattern such that the effects of the cooling water are uniformly distributed throughout the steam flow. Conversely, a non-uniform spray pattern of cooling water will result in an uneven and poorly controlled temperature reduction throughout the flow of the superheated steam. Along these lines, the inability of the cooling water spray to efficiently evaporate in the superheated steam flow may also result in an accumulation of cooling water within the steam pipe. The accumulation of this cooling water will eventually evaporate in a non-uniform heat exchange between the water and the superheated steam, resulting in a poorly controlled temperature reduction.
Various desuperheater devices have been developed in the prior art in an attempt to address the aforementioned needs. Such prior art devices include those which are disclosed in U.S. Pat. Nos. 6,746,001 (entitled Desuperheater Nozzle) and 7,028,994 (entitled Pressure Blast Pre-Filming Spray Nozzle), and U.S. Patent Publication No. 2006/0125126 (entitled Pressure Blast Pre-Filming Spray Nozzle), the disclosures of which are incorporated herein by reference. The present inventions represent an improvement over these and other prior art solutions, and provides a desuperheater device for spraying cooling water into a flow of superheated steam that is of simple construction with relatively few components and that requires a minimal amount of maintenance, is capable of spraying cooling water in a fine mist with very small droplets for more effective evaporation within the flow of superheated steam, and is capable of spraying cooling water in a geometrically uniform flow pattern for more even mixing throughout the flow of superheated steam. Various novel features of the present invention will be discussed in more detail below.